Field
The disclosure relates generally to a multi-phase switching regulator circuits and, more particularly, to a multi-phase switching regulator device having improved current sharing function thereof.
Description of the Related Art
Multi-phase switching regulators, sometimes known as a multi-phase switcher, is designed to distribute the output current evenly for each phase. In steady state operation, each phase has an equal amount of current. Some of the multi-phase switcher devices have the current sharing circuit which equalizes the current in each phase using a feedback mechanism. With equal current in each phase, the highest conversion efficiency is achieved when all phases are identical and symmetric; this is achieved with the same output stage switch, and the same inductor element.
In systems today, some of the multi-phase switch regulators have a “phase shedding” function. The phase shedding function reduces the number of active phases when the external load is light. For example, for the light load case, typically only one phase is operating, and all other phases will stop switching. In the multi-phase switch regulators, with phase shedding function, using the same inductor element for all the phases may be an optimum solution. For example, the efficiency can be improved using a low alternating current (AC) loss inductor during light load applications. During light load conditions, in phase 1 operation, the alternating current (AC) loss is dominated by inductor core loss. In contrast, usage of a low direct current (DC) loss inductor for the other phases improves the efficiency at heavy load conditions. For heavy load conditions, the conduction loss (e.g. IR loss) is dominant in the heavy load conditions.
Inductors are non-ideal and contain inductive, resistive and capacitive electrical characteristics. Different type of inductors typically have different DC and AC resistance. Current equalization in each phase of a multi-phase switch regulator is not optimum.
To illustrate the influence of resistance of inductor elements on multi-phase switch regulators, an example of a two-phase multi-phase switcher is shown. FIG. 1 illustrates two phases, Phase 1 5 and Phase 2 7, with an equivalent model of two inductors in parallel. The first phase current, Phase 1 5, is defined as I1 15. The second phase current, Phase 2 7, is defined as I2 25. The equivalent model for the first inductor is shown as resistor element R1 10, and inductor L1 20. The equivalent model for the second inductor is shown as resistor element R2 30, and inductor L2 40. The resistor R1 10, and resistor R2 30 include the inductor DC resistance and output switch resistance of switching regulators. The first and second current, I1 15 and I2 25, respectively sum to establish the output current I OUT, which flows into capacitor load C out 50 and Rload. The optimum current I1 15 and I2 25 to minimize the loss can be expressed as follows:I1=R2/(R1+R2)×IoutI2=R1/(R1+R2)×Iout
If the resistance R1 and resistance R2 are of equal magnitude, then the current is split equally between the two phases, will minimize DC resistive loss. If the resistance R1 and resistance R2 are non-identical (and not equal), DC resistance loss, the same I1 and I2 current will not minimize.
Concepts for detection and current balancing has been discussed in DC-DC converter circuits. U.S. Pat. No. 8,502,515 to Wan et al, describes a DC-DC converter having a load, a current detecting circuit and a channel current balance circuit.
Implementations to discuss proper ramping of current sharing also has been disclosed. U.S. Pat. No. 8,487,477 to Heineman shows a plurality of phases, a power stage, a feedback to balance the currents in the inductors. This circuit comprises a PID filter, a PWM, output control, power switches, load capacitor, and inductor and a feedback error amplifier to the PID filter.
Phase sharing has also been discussed in switching regulators. U.S. Pat. No. 8,405,368 to Laur et al. has a multiple phases, multiple loads, and a phase current sharing solution. The phase current sharing network includes conversion networks, and phase current combining networks.
Current balancing has also been discussed in multi-phase buck converters. U.S. Pat. No. 8,330,439 to Wu et al. shows a system and a methodology for current balancing in a multi-phase buck converter. The system includes power stages, inductors error amplifiers, PFM/PWM transition logic and power stage control logic.
Other concepts have also been proposed in multiple switch converters. U.S. Pat. No. 8,330,438 to Sreenivas et al. describes a means of a system and a methodology for current balancing in a multi-phase buck converter. The circuit comprises output voltage controller, and plurality of inductors, low pass filters, and phase balance networks.
It is desirable to provide a solution to address the disadvantages of current balancing and efficiency in a multi-phase switching regulator.